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Abstract

Aim:

To investigate the effect of sodium ascorbate (SA), an antioxidant and calcium hydroxide (Ca(OH)₂), a buffering agent mixture, on the shear bond strength of a luting resin to dentin, and pH changes of the extraradicular medium solution after intracoronal bleaching with hydrogen peroxide.

Materials and Methods:

In this in vitro study, 60 human maxillary central incisors were randomly assigned into six groups (n: 10): Group 1: restored, no bleach; group 2: bleached, bonded immediately; group 3: bleached, treated with 10% SA applications before bonding; group 4: bleached, treated with calcium hydroxide applications before bonding; group 5: bleached, treated with CaOH₂ and SA mixture applications before bonding; group 6: delay bonding by seven days. For bleach treatment in groups 2 to 6, intracoronal bleaching was performed with 35% hydrogen peroxide for four days. SA or CaOH₂ or mixture of SA and CaOH₂ were left in the access cavity for four days. Hybrid blocks, 4 mm × 4 mm wide × 2–mm thick, were luted with resin cements on dentin surface and then the specimens were subjected to shear bond strength testing. Analysis of variance and Tukey post hoc multiple comparison tests were applied (P < .05).

Results:

G2 and G4 showed significantly low bond strength values and they were lower than the other groups (P < .05). There were no significant differences between G1, G3, and G6 (P > .05). The pH values had risen markedly in the groups containing calcium hydroxide (G4 and G5) after four days (P < .05).

Conclusion:

The application of 10% SA or 10% SA and CaOH₂ mixture were effective at reversing bleaching effects on bond strength. CaOH₂ or CaOH₂ and 10% SA mixture increased the external medium pH and were effective for alkalinization after intracoronal bleaching.

Keywords

Sodium ascorbate Calcium hydroxide Shear bond strength Intracoronal bleaching

Introduction

Discoloration of endodontically treated teeth may occur because of intrapulpal hemorrhage, pulp necrosis, root canal sealer, gutta-percha remaining, and/or iatrogenic negligence at various stages of endodontic treatment. Discoloration caused by root canal treatment should be removed before ceramic laminate veneers treatment. Because veneers are generally fabricated with varying thicknesses ranging from 0.3 mm to 1 mm and reflect the underlying tooth color. Hydrogen peroxide (H₂O₂) and sodium perborate are used in intracoronal bleaching. Using 30% to 35% H₂O₂ in nonvital, discolored teeth has shown successful intracoronal bleaching in a short time.¹

Most of the results of bleaching studies for endodontically treated teeth were found sufficiently effectual, but a few studies stated some side effects of the bleaching therapy. The cervical resorption was common side effect for intracoronal bleaching therapy.^2,3 It is believed that intracoronal bleaching treatments decrease the pH and generate an inflammatory process around the teeth and implicate the cervical root resorption process.⁴ Therefore, a calcium hydroxide (Ca(OH)₂) dressing with a high pH (the pH value of the calcium hydroxide and glycerin mixture is close to 12)⁵ has been suggested in many studies to neutralize H₂O₂ and increase the pH during intracoronal bleaching procedures thus preventing cervical resorption.⁶

Another common side effect is the decreased bond strength.^7,8 The presence of residual oxygen and peroxide from the bleaching agent may provoke the decrement of the bonding strength in bleached teeth according to some bleaching studies.

This residual oxygen is thought to cause inhibition of resin polymerization.^9,10 The peroxide radicals affect peritubular and intertubular dentin, dissolving the organic part, increasing the permeability, and decreasing the hardness and elastic modulus.¹¹ In order to minimize this problem, it has been suggested to apply an antioxidant agent such as sodium ascorbate (SA)^12,13 between bleaching and restorative treatment, or delay the restorative process from one week to two weeks.^14,15

It is not known how mixing the agents used for the two most common complications after intracoronal bleaching will affect the expected benefit of the agents.

The aim of this study is to investigate the effect of SA, an antioxidant and calcium hydroxide, a buffering agent mixture, on the shear bond strength (SBS) of a luting resin to dentin, and pH changes of the extraradicular medium solution after intracoronal bleaching with H₂O₂. The null hypothesis of the study is that mixing SA and calcium hydroxide does not affect the expected benefits of the material.

Materials and Methods

Setting and Design

In order to perform the present in vitro study, 60 freshly extracted, erupted human maxillary central incisors were collected and stored in a solution of 0.5% Chloramine-T for three months at 4°C. Teeth with carious lesion and restoration, cracks caused during extraction, and developmental disorders that affect enamel and/or dentin were excluded from the study. Ethics Committee of Cukurova University Faculty of Medicine, dated November 13, 2020, numbered 45. Informed consent forms were signed by all patients. The procedures used in this study adhere to the tenets of the Declaration of Helsinki.

All teeth were sectioned on 3 mm apical to the cement–enamel junction with a diamond disc using a sectioning machine (Accutom 10, Struers, Rødovre, Denmark) under water. Standard endodontic access cavities were created by measuring with a bone caliper remaining 3 mm of dental tissue from the buccal middle triple with a 12 ≠ round medium grit diamond bur (Diatech, Coltene Whaledent, Altststten, Switzerland) with a high-speed hand piece under water cooling. Radiography confirmed that approximate 2-mm-dentin and 1-mm-enamel thickness remained in each tooth. The coronal pulp tissue was removed with a spoon excavator and medium grit diamond cavities were irrigated with 5 mL of 2.5% sodium hypochloride to dissolve organic tissues. A final flush with 2-mL saline solution was performed. The apical seal produced by 2-mm-thick layer of glass ionomer cement (Fuji IX, GC, Tokyo, Japan). The specimens were randomly divided into six groups (n = 10);

Group 1: The access cavity restorated with adhesive and composite resin. The universal adhesive (G-Premio Bond, GC, Tokyo, Japan) was applied on the etched dentin surfaces according to manufacturer’s instructions: after application of the adhesive, waiting for 10 s and using air pressure for 5 s with air spray and cured with 900 mW/cm² light intensity for 10 s (Elipar Freelight, 3M-ESPE, Minn, USA). And then the cavity was restored with 2-mm-thick vertical layer composite resins (GC, G-aenial, Tokyo, Japan) and 20-s light-cured.

Group 2: Intracoronal bleaching was performed with 35% H₂O₂ (Opalescence Endo, Ultradent Products Inc.). 0.03 mL of the respective bleaching agent was syringed into the access cavity, and the cavity was closed by glass ionomer cement (Fuji IX, GC, Tokyo, Japan) after placing a cotton pellet, and the specimens were stored in 100% humidity for four days. After the filling material and the cotton pellet were removed, the access cavity was rinsed with distilled water, and the final composite restoration was applied.

Group 3: Intracoronal bleaching procedure was repeated. The access cavity was rinsed with distilled water and dried with a cotton pallet, then SA paste was prepared by mixing 10% SA powder (Merck, Germany) with glycerin in ratio of 1 scoop/1 drop and was placed into the pulp chamber with lentulo and the cavity was closed by glass ionomer cement. SA paste was left into the pulp chamber for four days (equal of bleaching time)¹⁶ and then the specimens were rinsed for 1 min, and the final composite restoration was applied.

Group 4: Intracoronal bleaching procedure was repeated. The access cavity was rinsed with distilled water and dried with a cotton pallet, then calcium hydroxide paste was prepared by mixing calcium hydroxide powder with glycerin in ratio of 1 scoop/1 drop and was placed into the pulp chamber with lentulo and the cavity was closed by a temporary filling material. Calcium hydroxide paste was left in the access cavity for four days and then the specimens were rinsed for 1 min and the final composite restoration was applied.

Group 5: Intracoronal bleaching procedure was repeated. The access cavity was rinsed with distilled water, and dried with a cotton pallet, then a paste composed of 10% SA and calcium hydroxide was placed into the pulp chamber (1 scoop 10% SA powder + 1 scoop calcium hydroxide powder/2 drops glycerin), this paste was left in the access cavity for four days and then the specimens were rinsed for 1 min and the final composite restoration was applied.

Group 6: Intracoronal bleaching procedure was repeated. The access cavity was rinsed with distilled water, and dried with a cotton pallet, and then cavity was restorated with composite resin. Teeth were immersed in artificial saliva and allowed to stand for one week before veneer restoration.

pH Testing

Four cemental–dentinal defects were prepared just below the cemental–enamel junction (CEJ) on each root. The hemispherical defect (diameter 1.0 mm, depth 0.5 mm) was created using a round diamond bur (diameter 1.0 mm) in a high-speed handpiece. Each tooth was suspended in a plastic vial containing 20 mL of distilled water or saliva. The pH measurements were performed immediately (day 0) after immersion of the teeth. The pH was measured four days after the intracoronal bleaching procedure. During this period, the teeth were stored in the same medium without change of distilled water/saliva or bleaching material. Distilled water was replaced and the pH was measured four days after filling with calcium hydroxide or/and SA. The pH of the surrounding distilled water or saliva was evaluated on day 0, 4, and 8.

The pH meter ( PCE-PH 16, PCE Instruments, Germany) was calibrated with standard pH solutions before each experiment. For each sample, the average of two readings was utilized.

Shear Bond Strength Test

The buccal aspect of teeth were ground with 400 grit wet silicon carbide paper on a polishing machine (Exakt 400 cs Apparatebau, Norderstedt, Germany ), to obtain 4 mm × 4 mm flat, midcoronal dentin surface. A total of 60 hybrid blocks (Cerasmart, GC, Tokyo, Japan), measuring 4 mm × 4 mm wide × 2-mm-thick cubes were prepared with a diamond disk using a sectioning machine under water.

All prepareted hybrid block pieces were etched with 9.5% buffered hydrofluoric acid gel (Porcelain Etchant, Bisco, Schaumburg, IL, USA) for 90 s, rinsed with water, and carefully air-dried. Afterward, a primer (G-Multi Primer, GC, Tokyo, Japan) was applied for salinization of the etched restoration surfaces, and thinned with dry air spray.

A dual-polymerized resin cement (G-CEM Link Force. GC, Tokyo, Japan) was used for luting the restoration materials for all specimens. The resin cement was applied to the restoration surface. Soon after, the restoration material was pressed firmly on preparation surface of the tooth. Slightly hardened excess cement was carefully cleaned with microbrushes, and then 20-s light-cured.

The teeth were embedded horizontally into the acrylic resin making the buccal surface facing upwards. Shear load was applied in a direction parallel to the bonded interface via a universal testing machine (MOD Dental MIC-101, Esetron Smart Robototechnologies, Ankara, Turkey). The load speed was set at 0.5 mm/min and the loading was performed until failure occurred. The recorded shear bond force in newton was converted to megapascal (MPa) to symbolize the bond strength.

Statistical Analysis

The statistical analyses were performed using SPSS (IBM SPSS, Inc., Chicago, IL) 23.0 software. The data were normally distributed based on the results of the Shapiro–Wilk test (P > .05); thus, one-way analysis of variance was used for the SBS data analysis. The analysis of variance for repeated measurements was used for pH changes. Tukey post hoc test was used for the pairwise comparisons (P < .05). In order to see the pH changes in detail, the differences of pH values were taken for the measurements of day 0 and day 4, day 4 and day 8, and also on day 0 and day 8. These differences were analyzed by using one-way analysis of variance for group differences. The failure mode ratios were evaluated using the chi-squared test (P < .05).

Results

Bond Strength

Mean SBS values with standard deviation and differences between the groups are listed in Table 1. The analysis of variance indicated a statistically significant difference among the groups as a result of differences in sample treatment procedures (P = .000). Therefore, data were further analyzed by using the Tukey test for pairwise comparisons. There were no significant differences between the saliva (G6), negative control (G1), and ascorbic acid applied (G3, G6) groups (P = .072). G2 (bonded with composite resin immediately after bleaching), and G4 (calcium hydroxide applied) groups showed significantly low bond strength values and they were lower than the other groups (P = .001).

Table 1.

Means and Standard Deviations of the Shear Bond Strength Values (MPa)

Groups	n	Mean	SD
Positive control (G2)	10	4.85a	1. 09
Ca(OH)₂ (G4)	10	4.83a	1.23
Ca(OH)₂ + SA (G5)	10	7.66b	1.07
SA (G3)	10	7.80b	2.31
Saliva (G6)	10	8.62b	2.24
Negative control (G1)	10	9.29b	1.18

Note: Means for groups in nonhomogeneous subsets are displayed with different letters. Subset for alpha = 0.05.

Abbreviations: SD, Standard Deviation; Ca(OH)₂, Calcium Hydroxide; SA, Sodium Ascorbate.

Fracture Modes

The fracture modes of groups are shown in Table 2. In each group, mainly adhesive fractures were observed. The number of adhesive fracture modes was high in the immediately bonded after bleaching group (positive control). The number of cohesive type of fracture mode was high in the saliva and negative control group. There were no significant differences among the study groups in terms of fracture modes (P = .657).

Table 2.

Failure Mode (%) of the Groups

Groups	Adhesive*	Cohesive**	Mix***
Positive control (G2)	90	0	10
Ca(OH)₂ (G4)	80	0	20
Ca(OH)₂ + SA (G5)	70	0	30
SA (G3)	80	0	20
Saliva (G6)	60	10	30
Negative control (G1)	50	10	40

Note: *Adhesive failure, between the dentin and cement; **Cohesive failure, in dentin and/or ceramic and/or cement; *** Mix failure, which is combination of adhesive and cohesive failure.

pH Measurements

The pH changes of the extraradicular medium solution are summarized in Table 3. The base line pH values of the teeth in the groups are compatible with the pH of distilled water and saliva. Four days after the placement of bleaching agent, mean pH was recorded within a narrow band between pH 5.54 ± 0.12 and pH 5.86 ± 0.13 (Figure 1). Four days after placement of the calcium hydroxide paste, the pH values had risen markedly in the groups containing calcium hydroxide and were statistically different from the other groups (P < .001). At day 8, the mean differences of pH changes in groups using Ca(OH)₂ are statistically significant compared to other groups. (P < .001; Table 4)

Table 3.

Summary of pH of Extraradicular Medium Solution

Groups	Day 0		Day 4		Day 8
Groups	Mean	SD	Mean	SD	Mean	SD
Positive control (G2)	6.48a	0.31	5.68ab	0.34	6.47a	0.42
Ca(OH)₂ (G4)	6.59a	0.15	5.72bc	0.14	8.77b	0.75
Ca(OH)₂ + SA (G5)	6.55a	0.14	5.73bc	0.36	8.68b	0.68
SA (G3)	6.65a	0.12	5.71b	0.26	6.48a	0.34
Saliva (G6)	6.93b	0.60	5.86c	0.13	6.92a	0.26
Negative control (G1)	6.65a	0.11	5.54a	0.12	6.58a	0.36

Note: Means for groups in nonhomogeneous subsets are displayed with different letters. Subset for alpha = 0.05.

Abbreviations: SD, Standard Deviation; Ca(OH)₂, Calcium Hydroxide; SA, Sodium Ascorbate.

Figure 1.

The Mean Differences of pH Changes From Day 0 to Day 4, Day 0 to Day 8, and Day 4 to Day 8

Table 4.

The Mean Differences of pH Changes From Day 0 to Day 4, Day 0 to Day 8, and Day 4 to Day 8, Also Significances of Groups

Groups	n	Mean Difference Day (0–4)	SD	Sig.	Mean Difference Day (0–8)	SD	Sig.	Mean Difference Day (4–8)	SD	Sig.
Negative control (G1)	10	–1.10	0.08	a	–0.070	0.23	a	1.038	0.21	b
Positive control (G2)	10	–0.80	0.31	b	–0.013	0.26	a	0.792	0.16	a
SA (G3)	10	–0.95	0.20	ab	–0.185	0.18	a	0.769	0.14	a
Ca(OH)₂ (G4)	10	–0.87	0.22	ab	2.179	0.25	b	3.055	0.15	c
Ca(OH)₂ + SA (G5)	10	–0.81	0.24	b	2.129	0.27	b	2.942	0.27	c
Saliva (G6)	10	–1.04	0.14	ab	–0.005	0.11	a	1.044	0.10	b

Note: Means for groups in nonhomogeneous subsets are displayed with different letters. Subset for alpha = 0.05.

Abbreviations: SD, Standard Deviation; Ca(OH)₂, Calcium Hydroxide; SA, Sodium Ascorbate; Sig, Significance.

Discussion

One of the most undesirable effects observed in internal bleaching is cervical resorption and the other is compromised bond strength. There is a possibility of these two adverse effects to be seen together in intracoronal bleaching treatment. The current study assessed the effect of antioxidant and buffering agent mixture on dentin shear bond strengths of laminate veneer, and the pH change of external medium after intracoronal bleaching. Null hypothesis is not rejected. Mixing of 10% SA and calcium hydroxide did not adversely affect their expected benefits.

Several studies have recommended a time delay after bleaching to achieve optimum bond strength. However, there is no consensus on the exact time in the literature; some studies have been recommended for one week,^17,18 and some studies have reported that two weeks^19,20 or even three weeks^21,22 are required. As most of the studies suggested delaying for one week, in our study, the specimens in delayed group were immersed in artificial saliva solution for one week. Natural saliva which contains vitamin E and ascorbic acid acts as an oxidizer. In this study, it was shown that delay of one week increased the bond strength to the level of the nonbleached group. It is thought that during the storage of the samples in artificial saliva, the oxygen remaining in the dentin tissue is removed and the damaged dentin may be repaired.

Natural, nontoxic, and biocompatible SA activity is one of the most evaluated antioxidant after tooth bleaching. Several researchers reported that 10% SA is sufficient to reverse the reduction in bond strength for dentin and enamel after tooth whitening.^12,13,23,24 Therefore, 10% SA was preferred as an antioxidant in our study. In the recent study, the use of SA for equal of bleaching time was found to be sufficient to reverse the compromised bonding in the treated enamel.

The use of SA alone or mixed with calcium hydroxide increased the bond strength. There is no statistical difference between the two groups. The results of this study were well matched with the results of above mentioned studies; the bond strength for negative control and saliva groups were similar to the SA group’s strength.

Calcium hydroxide did not reduce the effect of SA. In this study, calcium hydroxide Ca(OH)₂ did not increase the bond strength when used alone. No significant difference was found between the calcium hydroxide Ca(OH)₂ and positive control groups.

The pH values of the samples at day 0 were compatible with the extraradicular medium. The pH values of samples stored in distilled water were between 6.65 ± 0.12 and 6.48 ± 0.31. The pH of the sample stored in saliva was 6.93 ± 0.60. There was significant reduction in the pH values after four days of intracoronal bleaching application in all samples. The pH of the 35% H₂O₂ gel used in the current study is 5.²⁵ Therefore, the use of H₂O₂ as an intracoronal bleaching agent decreased extraradicular pH in all groups. This study suggests that there was a pH change of the external medium, in agreement with the results of Rokaya et al.,²⁵ de Sá et al.,²⁶ and Lou et al.²⁷

Cai et al.²⁸ and Mustafa et al.²⁹ found that the pH of the dentin increases after placing calcium hydroxide Ca(OH)₂ in the root canal. de Sá al.²⁶ reported that calcium hydroxide increased the pH of external medium. They hypothesized that alkaline pH may interfere with osteoclastic activity and also stimulate hard tissue formation; therefore, it has a preventive effect on cervical resorption. In this study, calcium hydroxide or/and SA mixture dressing placed in the pulp chamber for buffering the acid pH created statistically significantly higher pH than the other groups. A 10% aqueous SA solution has a pH of 7.3 to 7.6. Therefore, it did not affect the pH of the highly alkaline calcium hydroxide. In the saliva group, the acidic pH reached near the initial value again via the buffering of saliva.

Today, intracoronal bleaching of nonvital discolorations is a common treatment. However, the presence of cement defects can increase the risk of cervical root resorption or causes low bond strength in adhesive restorations. A mixture of calcium hydroxide and SA can be considered as a dressing to avoid these two complications.

Conclusion

Treating the bleached dentin surfaces with 10% SA or a mixture of calcium hydroxide and SA, which reversed the compromised bond strength, were good alternatives to delayed bonding. Calcium hydroxide or a mixture of calcium hydroxide and SA increased the external medium pH and were effective for pH alkalinization after intracoronal bleaching.

Footnotes

Acknowledgements

The author would like to acknowledge Professor Dr Yuksel Bek, Department of Biostatistics and Medical Informatics, Ondokuz Mayis University, Turkey, for his assistance in statistical analysis.

Declaration of Conflicting Interests

The author declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author received no financial support for the research, authorship, and/or publication of this article.

References

Bersezio

, Ledezma

, Estay

, . Color regression and maintenance effect of intracoronal whitening on the quality of life: RCT-A one-year follow-up study. Oper Dent 2019; 44: 24–33.

Kandalgaonkar

, Gharat

, Tupsakhare

, . Invasive cervical resorption: A review. J Int Oral Health 2013; 5: 124–130.

Heithersay

, Dahlstrom

, and Marin

. Incidence of invasive cervical resorption in bleached root-filled teeth. Aust Dent J 1994; 39 82–87.

Dahlstrom

, Heithersay

, and Bridges

. Hydroxyl radical activity in thermo-catalytically bleached root-filled teeth. Endod Dent Traumatol 1997; 13: 119–125.

Athanassiadis

and Walsh

. Aspects of solvent chemistry for calcium hydroxide medicaments. Materials (Basel) 2017; 10: 1219.

Baratieri

, Ritter

, Monteiro

, . Nonvital tooth bleaching: Guidelines for the clinician. Quintessence Int 1995; 26: 597–603.

Shinohara

, Peris

, Pimenta

, . Shear bond strength evaluation of composite resin on enamel and dentin after nonvital bleaching. J Esthet Restor Dent 2005; 17: 22–29.

Jiang

, Lin

, Chen

, . Effects of remaining dentin thickness on the bond strength of bleached dentin. BMC Oral Health 2020; 20: 218.

Cadenaro

, Maravic

, Comba

, . The role of polymerization in adhesive dentistry. Dent Mater 2019; 35: e1–22.

10.

Vidhya

, Srinivasulu

, Sujatha

, . Effect of grape seed extract on the bond strength of bleached enamel. Oper Dent 2011; 36 433–438.

11.

Kawamoto

and Tsujimoto

. Effects of the hydroxyl radical and hydrogen peroxide on tooth bleaching. J Endod 2004; 30: 45–50, 53.

12.

Elawsya

, El-Shehawy

, and Zaghloul

. Influence of various antioxidants on micro-shear bond strength of resin composite to bleached enamel. J Esthet Restor Dent 2021; 33: 371–379.

13.

Bansal

, Kaur

, Cyriac

, . Impact of different antioxidants on the bond strength of resin based composite on bleached enamel-An in vitro study. J Contemp Dent Pract. 2019; 20:64–70.

14.

Topcu

, Erdemir

, Ozel

, . Influence of bleaching regimen and time elapsed on microtensile bond strength of resin composite to enamel. Contemp Clin Dent 2017; 8: 451–458.

15.

, Zhang

, Cheng

, . Effects of bleaching agents on dental restorative materials: A review of the literature and recommendation to dental practitioners and researchers. J Dent Sci 2015; 10: 345–351.

16.

Lai

, Mak

, Cheung

, . Reversal of compromised bonding to oxidized etched dentin. J Dent Res 2001; 80 1919–1924.

17.

Ismail

, Kilinc

, Hardigan

, . Effect of two-minute application of 35% sodium ascorbate on composite bond strength following bleaching. J Contemp Dent Pract 2017; 18: 874–880.

18.

Türkmen

, Güleryüz

, and Atalı

. Effect of sodium ascorbate and delayed treatment on the shear bond strength of composite resin to enamel following bleaching. Niger J Clin Pract 2016; 19: 91–98.

19.

de Almeida

, Lima

, Pereira

, . Influence of delay between dental bleaching with 35% hydrogen peroxide and orthodontic brackets on the bond strength at the enamel/adhesive interface. J Clin Exp Dent 2019, May 1; 11: e447–e451.

20.

Karadas

and Demirbuga

. Influence of a short-time antioxidant application on the dentin bond strength after intracoronal bleaching. Microsc Res Tech 2019; 82: 1720–1727.

21.

Cavalli

, Reis

, Giannini

, . The effect of elapsed time following bleaching on enamel bond strength of resin composite. Oper Dent 2001; 26: 597–602.

22.

Lai

, Tay

, Cheung

, . Reversal of compromised bonding in bleached enamel. J Dent Res 2002; 81 477–481.

23.

Ghaleb

, Orsini

, Putignano

, . The Effect of different bleaching protocols, used with and without sodium ascorbate, on bond strength between composite and enamel. Materials (Basel) 2020; 13: 2710.

24.

Cortez

, Ziotti

, Scatolin

, . Protocols for sodium ascorbate application on intracoronary dentin bleached with high-concentrated agent. J Conserv Dent 2018; 21: 26–31.

25.

Rokaya

, Beshr

, Mahram

, . Evaluation of extraradicular diffusion of hydrogen peroxide during intracoronal bleaching using different bleaching agents. Int J Dent 2015; 2015: 493795.

26.

, Jeronymo

, Yui

, . Effect of calcium hydroxide on pH changes of the external medium after intracoronal bleaching. J Contemp Dent Pract 2011; 12: 158–163.

27.

Lou

, Cathro

, Marino

, . Evaluation of hydroxyl radical diffusion and acidified thiourea as a scavenger during intracoronal bleaching. J Endod. 2016; 42:1126–1130.

28.

Cai

, Abbott

, and Castro

Salgado J

. pH changes in radicular dentine associated with calcium hydroxide and corticosteroid/antibiotic pastes. Aust Endod J 2018, May 13.

29.

Mustafa

, Alaajam

, Azeim

, . Diffusion of calcium hydroxide through dentinal tubules of retreated root canals: An in vitro study. Eur J Dent 2018; 12: 386–392.

Effect of Antioxidant and Buffering Agent Mixture on Dentin Shear Bond Strengths of Laminate Veneer and pH Change of External Medium After Intracoronal Bleaching

Abstract

Aim:

Materials and Methods:

Results:

Conclusion:

Keywords

Introduction

Materials and Methods

Setting and Design

pH Testing

Shear Bond Strength Test

Statistical Analysis

Results

Bond Strength

Fracture Modes

pH Measurements

The Mean Differences of pH Changes From Day 0 to Day 4, Day 0 to Day 8, and Day 4 to Day 8

Discussion

Conclusion

Footnotes

Acknowledgements

Declaration of Conflicting Interests

Funding

References